assistant2: Rework @mentions (#26983)

https://github.com/user-attachments/assets/167f753f-2775-4d31-bfef-55565e61e4bc

Release Notes:

- N/A

crates/project/src/lsp_store.rs

@@ -7872,6 +7872,7 @@ impl LspStore {
                         runs: Default::default(),
                         filter_range: Default::default(),
                     },
+                    icon_path: None,
                     confirm: None,
                 }]))),
                 0,
@@ -9098,6 +9099,7 @@ async fn populate_labels_for_completions(
                     old_range: completion.old_range,
                     new_text: completion.new_text,
                     source: completion.source,
+                    icon_path: None,
                     confirm: None,
                 });
             }
@@ -9110,6 +9112,7 @@ async fn populate_labels_for_completions(
                     old_range: completion.old_range,
                     new_text: completion.new_text,
                     source: completion.source,
+                    icon_path: None,
                     confirm: None,
                 });
             }

crates/project/src/project.rs

@@ -390,6 +390,8 @@ pub struct Completion {
     pub documentation: Option<CompletionDocumentation>,
     /// Completion data source which it was constructed from.
     pub source: CompletionSource,
+    /// A path to an icon for this completion that is shown in the menu.
+    pub icon_path: Option<SharedString>,
     /// An optional callback to invoke when this completion is confirmed.
     /// Returns, whether new completions should be retriggered after the current one.
     /// If `true` is returned, the editor will show a new completion menu after this completion is confirmed.